1. Field of the Invention
This invention relates to a lubricating oil composition and, more specifically, it relates to a lubricating oil composition for use in apparatuses such as compressors and other than food processing machines.
2. Prior Art
Compressed air used in the specific fields, such as the food and its associated industry, medical instruments, pharmaceutical industry and medical care, which are considered to have effects on human bodies, has generally been produced by the combined use of an oil-cooled compressor and a mist filter. Oil-free type compressors have now a power of 15 kW even if they are very small and the apparatus cost is at least about two times as high as the oil-cooled compressor, and therefore, there are few cases in which small- and medium-scale manufactories or medical institutions use such oil-free type compressors.
The circumstances under which compressed air is contacted with human bodies and considered to have effects thereon, include agitation of ice cream and like foodstuffs with compressed air; peeling of onion and like vegetables (instantaneous blowing-off of vegetable skins with compressed air); stirring of soybean and like foods which are in the process of fermentation, with compressed air; blowing-off of the portion of a refreshing drink or an alcoholic beverage spilt around the mouth of the bottles at the time of filling the bottles with said liquid; cleaning of bottles with compressed air; transportation of sugar and like powders with compressed air; the use of compressed air as an air source for dentists' hand air-drill; and cleaning of oral cavities with compressed air. In a case where compressed air produced by the combined use of an oil-cooled compressor and a mist filter is to be used under various circumstances, it will be very difficult to completely remove the oil mist from the compressed air over a long period of time, and there are possibilities that several p.p.m. to several tens of p.p.m. of the oil will be discharged to the outside of the system.
Further, a screw type compressor has generally been used to compress CO.sub.2 gas so as to produce dry ice therefrom in small- and medium-scale factories. A lubricating oil used in the compressor in this case is lubricating the compressor while the oil is in direct contact with it, and, therefore, the lubricating oil should be one whose safety for human bodies has been taken into consideration from the standpoint of the use of dry ice. Additionally, the lubricating oil is required to have oxidation resistance since it is incorporated with a minute amount of air. For this reason, lubricating oils for a compressor which have heretofore been used for the above purpose, include animal and vegetable oils having high safety and liquid paraffin. However, these conventional oils and liquid paraffin raise problems as to insufficient rust preventiveness and oxidation stability.
Accordingly, no oils having high safety for such apparatuses as compressors and also having excellent oxidation stability, rust preventiveness and lubricity, have been developed and therefore, the conventional lubricating oils have had various problems to be solved before the accomplishment of the present invention.